A multi-agency operation designed to crack down on sexual offences on London's public transport has resulted in 15 arrests in a single week.

The operation, held from 23-28 September, was part of Project Guardian, a collaborative effort by the British Transport police, Metropolitan police, City of London police and Transport for London. It involved 120 plain-clothed and uniformed officers carrying out daily patrols.

Project Guardian was formed in April, after a TfL survey revealed that 15% of women and girls had experienced unwanted sexual behaviour on the transport network, but 90% of them had not reported it. The aim of the initiative was to improve levels of reporting of sexual offences, and to create an environment on public transport that does not tolerate intimidation and sexual harassment.

Since the public launch of Project Guardian earlier this year, there has been a 20% increase in the reporting of sexual offences on the transport network compared with the same period last year. From 1 April to 31 August there was a 32% increase in the detection of sexual offences, with 170 detections. (Detections occur when an offender is charged or summonsed, or receives a caution, reprimand or warning.)

Supt Nicki Watson of the British Transport police said: "It's very encouraging to see that since the launch of Project Guardian, more victims are coming forward to report what's happened to them, and more offenders are being caught. Despite these good results we must not become complacent, and will be working hard to further tackle inappropriate sexual behaviour on London's transport network.

"We want victims to know that all reports are taken seriously, and we'll do everything we can to bring offenders to justice. If someone has made you feel uncomfortable on your tube, rail or bus journey – however minor it may seem to you – reporting it to police can help us target the perpetrator and prevent it happening to another passenger."

An online awareness-raising campaign was carried out on Twitter by the British Transport police and the Everyday Sexism Project during the week of action. Experiences reported by Twitter users included:

Ch Supt Sultan Taylor from the Met's safer transport command said: "Our primary aim is to safeguard the travelling public and we will be tirelessly carrying out patrols and investigations, using all manner of policing tactics at our disposal, to disrupt sexual offenders operating on the transport network in London.

"We want to make sure that any kind of sexual offence that occurs on the transport network is investigated, and I would urge people to immediately come forward and report their concerns to the police to enable us to bring offenders to justice."

Anne Medlycott, assistant DI for the City of London police's public protection unit, said: "Project Guardian continues to do an excellent job promoting prevention and the detection of sexual offences that would have otherwise gone unreported. The week of action has shown how successful a joint approach can be, and the City of London police is proud to be a part of it."

• To report an incident of a sexual nature to British Transport police, call 0800 40 50 40 or text 61016 with details of what happened. For an incident that has occurred away from the railway network, call 101. In an emergency, always dial 999.